Glassey U.S. Pat. No. 3,532,102 discloses a blending control system which controls one of the two liquids being fed into a mixing chamber so that the blended product is controlled to any of a number of parameters such as density, consistency, pH.
Smith, U.S. Pat. No. 3,499,580 discloses a pressure pour apparatus and component. To obtain an indication of the pressure forcing the liquid up the discharge passageway, a bubbler tube is provided with its open exit end located below the surface of the liquid. So long as bubbles continue to emerge from the bubbler tube, the pressure in the tube is essentially an indicator of the pressure in the liquid at the submerged end of the tube and hence, by accounting for the difference in elevation between that submerged end and the submerged end of the discharge passageway, can be used as an indicator of the pressure in the liquid acting to force the liquid up the discharge passageway. Note col. 1 lines 54-64.
Kroll et al U.S. Pat. No. 2,886,051 discloses a control of density of a homogenous mixture of liquid and solid material such as ore in water. Kroll et al disclose that the majority of systems arranged to measure the density of this mixture in classifiers employ bubble-tubes as primary elements.
Vetter U.S. Pat. No. 2,577,548 discloses compensated specific gravity measuring.
Khoi U.S. Pat. No. 4,006,635 discloses a liquid level measuring process and indicator using two hydrostatic probes for spray, the first probe emerging near the bottom of the tank and the second slightly below the maximum filling level. A pressure differential/electric voltage transducer is connected to the probes.
Hopfe et al U.S. Pat. No. 3,613,456 discloses a bubbler method and apparatus comprising at least one pair of bubbler pipes wherein humidified gas is used as the bubbler fluid.
Cooper U.S. Pat. No. 3,551,897 discloses a method of controlling ore flotation using an analog or digital computer to optimize various measured parameters.
Davis et al U.S. Pat. No. 4,252,139 discloses a method and apparatus for automatically mixing a solution having a specified concentration. Davis et al are directed to the formation of Glauber salt.
Eidschun U.S. Pat. No. 4,393,705 discloses an apparatus which utilizes pipes of different lengths oriented vertically within the fluid of a reservoir which are constantly pressured with a gas source, normally air, for the measurement of the specific gravity of and calculation of the level of the liquid in the reservoir.
Carr et al, "State-of-the-Art Assessment of Coal Preparation Plant Automation", ORNL-3699, U.S. Department of Energy (February 1982) pp. 48-52 discloses adjustment of tailings flow to control liquid level, as measured by a single-leg dip tube, in a froth flotation beneficiation of coal.
C. H. Wells, "Control Systems in Coal Preparation Plants", Report CS-1880 by Envirotech Corporation for Electric Power Research Institute (June 1981) pp. 4-25 through 4-32 recognizes the desirability of reducing shortterm fluctuations in froth flotation of coal by utilizing feedback control from on-line measurements, and discusses manipulation of several process variables responsive to measurement of various parameters.